1. Field of the Invention
The present invention relates to an apparatus for processing an audio signal and method thereof. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for encoding or decoding audio signals.
2. Discussion of the Related Art
Generally, an audio signal has correlation between a low frequency band signal and a high frequency band signal within one frame. In consideration of the principle of the correlation, it is able to compress an audio signal by a band extension technology that encodes high frequency band spectral data using low frequency band spectral data.
However, in the related art, in case that low correlation exists between a low frequency band signal and a high frequency band signal, if an audio signal is compressed using a band extension scheme, a sound quality of the audio signal is degraded.
Specifically, in case of sibilant or the like, since the correlation is not high, the band extension scheme for the audio signal is not suitable for the sibilant or the like.
Meanwhile, there are band extension schemes of various types. A type of a band extension scheme applied to an audio signal may differ according to a time. In this case, a sound quality may be instantly degraded in an interval where a different type varies.